Interviewing at Amazon is a tiring experience. It started out with 2 rounds of phone interviews with the hiring manager and a Director of Engineering. They felt I met the minimum standards and called me on site for a round of face-to-face interviews.
I had 6 different interviews during the day, all of which were extremely technical and full of details. Most of the interviews related to designing APIs, writing functional specifications... The two people who interviewed me over the phone also interviewed me in person. Plus 4 others.
The experience was pleasant, but tiring. I suggest you get plenty of rest before the interview and go prepared for a grueling day.